linux-kernel - Re: [PATCH] mm: cma: Discard clean pages during contiguous allocation instead of migration

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Date:	Tue, 11 Sep 2012 09:59:49 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Kyungmin Park <kmpark@...radead.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH] mm: cma: Discard clean pages during contiguous
 allocation instead of migration

On Tue, Sep 11, 2012 at 09:41:52AM +0900, Minchan Kim wrote:
> This patch drops clean cache pages instead of migration during
> alloc_contig_range() to minimise allocation latency by reducing the amount
> of migration is necessary. It's useful for CMA because latency of migration
> is more important than evicting the background processes working set.
> In addition, as pages are reclaimed then fewer free pages for migration
> targets are required so it avoids memory reclaiming to get free pages,
> which is a contributory factor to increased latency.
> 
> * from v1
>   * drop migrate_mode_t
>   * add reclaim_clean_pages_from_list instad of MIGRATE_DISCARD support - Mel
> 
> I measured elapsed time of __alloc_contig_migrate_range which migrates
> 10M in 40M movable zone in QEMU machine.
> 
> Before - 146ms, After - 7ms
> 
> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> Cc: Michal Nazarewicz <mina86@...a86.com>
> Cc: Rik van Riel <riel@...hat.com>
> Signed-off-by: Mel Gorman <mgorman@...e.de>
> Signed-off-by: Minchan Kim <minchan@...nel.org>

My signed-off is already on this but in earlier versions I was still
asking for changes. This time the patch looks good to me so even though
it is a bit redundant.

Reviewed-by: Mel Gorman <mgorman@...e.de>

Thanks Minchan.

-- 
Mel Gorman
SUSE Labs
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